Field devices such as vortex flowmeters are commonly used in industrial processes to measure a flow of process fluid, such as slurries, liquids, vapors and gases of chemicals, petroleum, pharmaceuticals, food and other fluid-type plant processes. Typically, vortex flowmeters utilize a shedding bar placed in a fluid flow to cause or generate vortices on opposite sides of the shedding bar. The frequency of vortex shedding for a shedding bar is directly proportional to the velocity of flow in the process fluid. Therefore, vortex flowmeters sense the fluctuating pressures caused by the generated vortices to determine the velocity of the process fluid flow. Example vortex flowmeter implementations can be found in U.S. Pat. No. 4,926,695 to Rosemount Inc., of Eden Prairie, Minn. on May 2, 1990; and U.S. Pat. No. 5,343,762 to Rosemount Inc., of Eden Prairie, Minn. on Sep. 6, 1994, both of which are commonly assigned with the present application.
Piezoelectric crystal-based sensors are commonly used in field devices, such as vortex flowmeters, to detect small mechanical motions, such as those created by vortices in a vortex flowmeter. Because these meters are used in industrial environments, the crystals are commonly sealed in a steel body to protect them from the environment. Since the piezoelectric based-crystals are susceptible to certain reducing atmospheres, these steel bodies in which such crystals are placed, are frequently pre-oxidized to prevent a severe reducing atmosphere from forming within the steel bodies. In practice, sealing piezoelectric-based crystals in pre-oxidized steel bodies may not always be effective. Specifically, over time, the piezoelectric crystals may fail in some high-temperature applications. Accordingly, embodiments of the present invention are generally directed to increasing the longevity of piezoelectric-based crystals in high-temperature industrial monitoring and control applications.